Comparative sensitivity of four methods for measuring changes in respiratory flow resistance in man.

Four methods for measuring human respiratory flow resistance were compared. Respiratory flow resistance changes were induced in nine subjects by breathing of 10 to 16 parts per million sulfur-dioxide. Before, during and after exposure to sulfur-dioxide flow resistance measurements were made by esophageal catheter, plethysmograph, forced pressure oscillation and airway interruption. The absolute increase in flow resistance in response to sulfur-dioxide decreased as a function of the frequency of measurement. There was an increase in lung volume and in transpulmonary pressure accompanying rapid breathing. Once the variable of error of each method and the volume history of the lungs prior to each measurement were taken into account, all methods showed comparable sensitivities, except for the interruption method. The authors conclude that the fact that changes were smaller for measurements obtained at higher cycling frequencies, has practical importance when choosing a method of study.